1. Field of the Invention
The present invention pertains to limiting the maximum tension in a string of drill pipe or other member suspended from a floating vessel and which may be subjected to stresses of magnitudes that could cause the pipe to yield or even fail.
2. Description of the Prior Art
As the demand for hydrocarbons has increased, the search for crude oil and natural gas has been extended further out into the sea. With increasing water depths, more and more drilling is conducted from floating vessels. A number of problems are encountered in floating drilling operations as a result of vessel motions caused by wind, waves and currents. Vertical movements of the vessel pose particularly severe problems. For most drilling operations, however, vessel heave is compensated for by the use of slip joints positioned in the suspended tubular members, permitting them to extend rather than become overstressed.
At times, drilling procedures must be performed which render the telescoping joints of little use in alleviating pipe stresses caused by vertical motion. For example, a number of operations require the drilling rig to pull upward on an apparatus or other load which is anchored to the sea floor. This may result from the apparatus being stuck, allowing no vertical movement, or restrained by design, allowing only limited vertical movement. When using the suspended pipe string to pull upward on such apparatus, all of the slip joints will, of course, be fully extended. In such a case, there is a significant risk that the suspended pipe string may be excessively stressed, especially if the floating vessel suddenly heaves upward due to wind or wave action. Not only could the excessive stress cause the suspended pipe string to yield or even fail, but it also could damage the subsea apparatus. Therefore, there exists a need for an apparatus that will limit the maximum tension which can be imposed on a suspended pipe string.